What is the hairs most characteristic forensic feature when viewed under a microscope?

The hair's most characteristic forensic feature when viewed under a microscope is morphology.

Explanation:

One of the most important resources in the forensic analysis of crime scenes are hair samples. They often provide useful information in trying to identify a suspect or victim. The features which are examined when observing a hair under a microscope are the cuticle, medulla, cortex, and root. The main purpose for examining a hair found at a crime scene is to determine if it is human or animal, for example, and then match it to a victim. In order to test a hair for DNA the root must be present. While hair shape and texture are influenced by our genes, to get accurate DNA evidence the root of the hair needs to be present.